As the integration of semiconductor devices increases, multi-layer interconnection technology has been put into practical use. Thus, local and global area planarization of an interlayer insulating layer has become important. A widely used CMP (Chemical Mechanical Polishing) method of polishing the surface of a semiconductor wafer employs chemical components contained in a slurry solution, a polishing pad, and a polishing agent.
A CMP apparatus is most frequently used to polish the front face of a semiconductor wafer in fabricating semiconductor devices on the wafer. Generally, a wafer is planarized or softened at least one time during the fabricating process in order to make the surface of the wafer as flat as possible. In order to polish the wafer, the wafer is placed on a carrier, put into contact with a polishing pad covered with slurry and then pressed. Wafer polishing is then carried out by rotating the polishing pad and the wafer-loaded carrier.
A prior art CMP apparatus for polishing a wafer includes a polishing platen, a polishing pad located over the polishing platen, a polishing head, and a retainer ring and/or membrane for holding the wafer in the bottom edge of the polishing head. The wafer is held in the retainer ring so that the surface of the wafer to be polished is disposed toward the polishing pad. The retainer ring has multiple grooves to facilitate the flow of polishing slurry to the surface of the wafer. The grooves are extended from the inner to the outer surface of the retainer ring. Each groove has a round shape structure.
We will now look at the way in which the retainer ring and polishing pad are used in the prior art. To this end, FIG. 1a through FIG. 1c are schematic, cross-sectional, views which illustrate a retainer ring of a prior art polishing head. FIG. 1a is a schematic, cross-sectional, view illustrating the structure of a prior art CMP polishing head 18 for polishing the surface of a wafer. FIG. 1b and FIG. 1c are schematic, cross-sectional, views which illustrate the retainer ring 14. FIG. 1c is a cross-sectional view of the channels 16 of the retainer ring 14 depicted in FIG. 1b. 
Referring to FIG. 1a, the prior art CMP apparatus has a polishing pad 10 which is covered with the flow of polishing slurry. It also has a polishing head 18. The wafer 12 is positioned between the polishing pad 10 and the polishing head 18. A retainer ring 14 is disposed at the bottom edge of the polishing head 18. The retainer ring 14 holds the wafer 12 to prevent it from being derailed during the CMP process. The retainer ring 14 of the polishing head 18 has multiple grooves 16 to facilitate the flow of polishing slurry. The grooves 16 are extended from the inner surface of the retainer ring 14 to the outer surface of the retainer ring 14. The slurry flows uniformly on the surface of the wafer 12, since the grooves 16 act as passing channels to facilitate the flow of polishing slurry.
FIG. 1b is a cross-sectional bottom view of the retainer ring 14. As mentioned above, the retainer ring 14 has multiple grooves 16 which extend from its inner surface to its outer surface. As shown in FIG. 1b, the grooves 16 are circularly shaped and skewed at a predetermined angle toward the outer rim against the rotating direction of the retainer ring 14. During a polishing process, the retainer ring 14 rotates with the desired speed and provides the whole area of the wafer 12 with a uniform flow of the polishing slurry through the grooves 16.
As shown in FIG. 1c, the cross-sections of the channels 16 have a round shape 16a. Thus, the channels 16 facilitate the smooth flow of polishing slurry over the surface of the wafer in comparison with the rectangular shape of grooves sometimes employed in the prior art. The worn amount of the polishing pad may be reduced by preventing fast sticking of the polishing pad, so that the durability of the pad can be increased.
Conventional CMP polishing heads have employed consumables such as a retainer ring or membrane, but these consumables cause a huge increase in maintenance costs.
Volodarsky et al., U.S. Pat. No. 5,803,799, describes a polishing head for polishing a semiconductor wafer. The polishing head includes a housing, a wafer carrier movably mounted to the housing, and a wafer retainer movably mounted to the housing.
Quek et al., U.S. Pat. No. 6,245,193, describes a substrate carrier head for use in a CMP apparatus.
Park et al., U.S. Pat. No. 6,336,846, describes a chemical-mechanical polishing (CMP) apparatus having a polishing head onto which a semiconductor wafer is fixed for holding the surface of the semiconductor wafer in contact with the surface of a polishing pad.